One approach to using unlicensed radio frequency (RF) spectrum to deliver Long-Term Evolution (LTE) wireless service is referred to as “LTE and Wi-Fi Link Aggregation” or just “LWA.” LWA has been proposed as an alternative to other schemes for using unlicensed RF spectrum to provide LTE wireless service, such as Long Term Evolution Unlicensed (LTE-U) and Licensed Assisted Access LTE (LAA).
With LWA, an LTE base station (also referred to as an “eNodeB”) communicates user data that is intended for a given item of user equipment (UE) to the wireless local area network (WLAN) infrastructure. The WLAN infrastructure in turn wirelessly transmits the user data to the UE using unlicensed RF spectrum and the relevant WLAN (IEEE 802.11) protocols. The LTE eNodeB also transmits user data to the UE using licensed RF spectrum. That is, both a licensed LTE link and an unlicensed WLAN link are used together (that is, are “aggregated”) to wirelessly transmit downstream user data to the UE. With LWA, signaling is communicated between the LTE eNodeB and the UE using the licensed LTE link. Since the LTE user data is transmitted by the WLAN infrastructure using WLAN protocols, the LTE user data acts like any other WLAN traffic when transmitted using LWA.
In LWA, a special interface, the “Xw” interface, is used to communicate control and user data between an eNodeB (the “anchor”) and the WLAN infrastructure. The logical node that, from the perspective of an LTE eNodeB, terminates the Xw interface is referred to as the “wireless termination” (WT). The WT can be implemented using a single WiFi access point (AP) or with a WLAN access controller (AC) that communicates with a group of WLAN APs.
LWA is often used in deployments where a group of small cell base stations are used to provide LTE service in a particular coverage area (for example, in “in-building” applications).
FIG. 1 is a block diagram illustrating one non-collocated example of an LWA small cell deployment. In this example, multiple small cells 102 are deployed throughout a coverage area. Each small cell 102 is coupled to the wireless operator's core network via an Internet Protocol (IP) network (for example, via an IP connection implemented using an Ethernet local area network (LAN) and an Internet connection).
Each small cell 102 is configured to use LWA to communicate with user equipment (UE) 104. Each small cell 102 communicates with a wireless termination (WT) using the LWA Xw interface. In the example shown in FIG. 1, the WT is implemented using a WLAN AC 106 that communicates with a group of WLAN APs 108 that are distributed throughout the coverage area. The WLAN AC 106 is communicatively coupled to the WLAN APs 108 and the small cells 102 via, for example, an IP network (for example, the Ethernet LAN to which the small cells 102 are otherwise connected). This is typical in in-building small cell deployments. Each small cell 102 has an associated LWA mobility group 110.
In this example, the WT is not co-located with small cells 102.
FIG. 2 is a block diagram illustrating a collocated example of an LWA small cell deployment. In this example, each small cell 202 is integrated with a WLAN AP 208. Otherwise, the example shown in FIG. 2 is similar to the one shown in FIG. 1.
With such small-cell-LWA deployments, a separate Xw interface and LWA mobility group is implemented for each small cell. As a result, in large deployments with many small cells, a large number of Xw interfaces and LWA mobility groups will need to be implemented and managed. Also, as a UE moves throughout the coverage area, it will pass through many LWA mobility groups. The overhead associated with tracking each UE and determining the appropriate LWA mobility group increases as the number of small cells increases. Moreover, gaps in LWA coverage can result due to differences in the hand-over boundaries of the unlicensed-spectrum coverage areas of the APs and the hand-over boundaries of the licensed-spectrum coverage areas of the small cells.
Furthermore, where a centralized WLAN AC is used, the user traffic for each Xw interface is often communicated from the respective small cell, to the WLAN AC, and then to the appropriate WLAN AP. This can result in the “hairpinning” of the user traffic as it flows from a remotely located small cell, to the centrally located WLAN AC, and then back to the remotely located WLAN AP.